Proteins having clinical or industrial value may be obtained using techniques which facilitate their synthesis in bacterial or in eukaryotic cell cultures. However, once synthesized, there are often problems in recovering these recombinant proteins in substantial yields and in a useful form. For example, recombinant proteins expressed in bacteria often accumulate in the bacterial cytoplasm as insoluble aggregates known as inclusion bodies [Marston, (1986) Biochem. J. 240:1-12; Schein (1989) Biotechnology 7:1141-1149]. Similarly, recombinant transmembrane proteins which contain both hydrophobic and hydrophilic regions are intractable to solubilization.
While transmembrane recombinant proteins and recombinant proteins which are expressed in the cytoplasm may be solubilized by use of strong denaturing solutions (e.g., urea, guanidium salts, detergents, Triton, SDS detergents, etc.), solubilization efficiency is nevertheless variable and there is no general method of solubilization which works for most proteins. Additionally, many proteins which are present at high concentrations precipitate out of solution when the solubilizing agent is removed. Yet a further drawback to solubilization of recombinant proteins is that denaturing chemicals (e.g., guanidium salts and urea) contain reactive primary amines which swamp those of the protein, thus interfering with the protein's reactive amine groups.
Thus, what is needed is a method for producing soluble proteins.